[A case of recurrent cerebral vein thrombosis with protein C gene mutation identified]

We reported a 31-year-old man with recurrent cerebral venous thrombosis caused by congenital protein C deficiency. He was diagnosed with cerebral venous thrombosis before 7 months. He was transferred to our hospital with numbness of right hand and right side of face, and dysarthria. The blood examination showed that his protein C antigen level and protein C activity were decreased than the lower limits of normal. Brain magnetic resonance venography showed poor visualization of the superior sagittal sinus and cortical veins. Genetic analysis revealed a single-base substitution (C>T) at the codon 811 (Arg to Trp) in the 9th exon portion of the protein C gene. Taking those results, he was diagnosed with recurrent cerebral venous thrombosis due to congenital protein C deficiency. Cerebral venous sinus thrombosis that occurred in the absence of an incidents of disease or internal history when there is a juvenile onset, a past history, or a family history, is suspected of congenital thrombophilia and needs blood tests and genetic tests.

Do prothrombotic factors influence clinical phenotype of severe haemophilia? A review of the literature

There is considerable variability in bleeding patterns of severe haemophilia (<1% factor VIII). Knowledge of the contribution of thrombophilic factors in these patterns may improve individually tailored treatment strategies. We reviewed the literature regarding the relation between prothrombotic factors and clinical phenotype of severe haemophilia. Medline and EMBASE were searched for relevant articles. 9369 articles published between 1963 and September 2003 were screened and seven relevant papers were retrieved. Each of these reported on a different combination of thrombophilic factors. Presence of the factor V Leiden mutation appears to decrease the severity of severe haemophilia most consistently. Findings on other thrombophilic factors were inconclusive. There is a clear need for additional research on potential determinants of phenotypes of severe haemophilia before such knowledge can be translated into individual care for severe haemophilia patients with confidence.

The prevalence and clinical manifestation of hereditary thrombophilia in Korean patients with unprovoked venous thromboembolisms

Background

Hereditary thrombophilia (HT) is a genetic predisposition to thrombosis. Asian mutation spectrum of HT is different from Western ones. We investigated the incidence and clinical characteristics of HT in Korean patients with unprovoked venous thromboembolism (VTE).

Methods

Among 369 consecutive patients with thromboembolic event who underwent thrombophilia tests, we enrolled 222 patients diagnosed with unprovoked VTE. The presence of HT was confirmed by DNA sequencing of the genes that cause deficits in natural anticoagulants (NAs). Median follow-up duration was 40±38 months.

Results

Among the 222 patients with unprovoked VTE, 66 (29.7%) demonstrated decreased NA level, and 33 (14.9%) were finally confirmed to have HT in a genetic molecular test. Antithrombin III deficiency (6.3%) was most frequently detected, followed by protein C deficiency (5.4%), protein S deficiency (1.8%), and dysplasminogenemia (1.4%). The HT group was significantly younger (37 [32–50] vs. 52 [43–65] years; P < 0.001) and had a higher proportion of male (69.7% vs. 47%; P = 0.013), more previous VTE events (57.6% vs. 31.7%; P = 0.004), and a greater family history of VTE (43.8% vs. 1.9%; P < 0.001) than the non-HT group. Age <45 years and a family history of VTE were independent predictors for unprovoked VTE with HT (odds ratio, 9.435 [2.45–36.35]; P = 0.001 and 92.667 [14.95–574.29]; P < 0.001).

Conclusions

About 15% of patients with unprovoked VTE had HT. A positive family history of VTE and age <45 years were independent predictors for unprovoked VTE caused by HT.

The clinical presentation and genotype of protein C deficiency with double mutations of the protein C gene

BACKGROUND

Severe protein C (PC) deficiency is a rare heritable thrombophilia leading to thromboembolic events during the neonatal period. It remains unclear how individuals with complete PC gene (PROC) defects develop or escape neonatal stroke or purpura fulminans (PF).

PROCEDURE

We studied the onset of disease and the genotype of 22 PC-deficient patients with double mutations in PROC based on our cohort (n = 12) and the previous reports (n = 10) in Japan.

RESULTS

Twenty-two patients in 20 unrelated families had 4 homozygous and 18 compound heterozygous mutations. Sixteen newborns presented with PF (n = 11, 69%), intracranial thromboembolism and hemorrhage (n = 13, 81%), or both (n = 8, 50%), with most showing a plasma PC activity of <10%. Six others first developed overt thromboembolism when they were over 15 years of age, showing a median PC activity of 31% (range: 19-52%). Fifteen of the 22 patients (68%) had the five major mutations (G423VfsX82, V339M, R211W, M406I, and F181V) or two others (E68K and K193del) that have been reported in Japan. Three of the six late-onset cases, but none of the 16 neonatal cases, had the K193del mutation, which has been reported to be the most common variant of Chinese thrombophilia. A novel mutation of A309V was determined in a family of two patients with late onset.

CONCLUSIONS

The genotype of double-PROC mutants might show less diversity than heterozygous mutants in terms of the timing of the onset of thrombophilia (newborn onset or late onset).

Genetic characterization of antithrombin, protein C, and protein S deficiencies in Polish patients

INTRODUCTION    Inherited deficiencies of natural anticoagulants such as antithrombin (AT; gene: SERPINC1), protein C (PC; PROC), and protein S (PS; PROS1), with the prevalence in the general European population of 0.02% to 0.17%, 0.2% to 0.3%, and 0.5%, respectively, are associated with increased risk of thromboembolic events. Only a few case reports of Polish deficient patients with known causal mutations have been published so far. OBJECTIVES    The aim of the study was to characterize the frequency of SERPINC1, PROC, and PROS1 mutations and their thromboembolic manifestations in patients with AT, PC, or PS deficiencies, inhabiting southern Poland. PATIENTS AND METHODS     Ninety unrelated patients (mean [SD] age, 40.1 [13.2] years) with AT (n = 35), PC (n = 28), or PS (n = 27) deficiencies, with a history of venous 73 (81%) or arterial 17 (19%) thromboembolism, were screened for mutations using the Sanger sequencing or multiplex ligation‑dependent probe amplification. RESULTS    Twenty mutations (29%) described here were new, mostly in the SERPINC1 and PROC genes. Missense mutations accounted for 84% of all mutations in the PROC gene and approximately 50% of those in the SERPINC1 and PROS1 genes. In all 3 genes, the ratio of nonsense and splice-site mutations was 8% to 31% and 8% to 23%, respectively. The mutation detection rate was 90% for AT or PC when anticoagulant activity was below 70%, while for the PROS1 gene, the rate reached 80% at the free PS levels below 40%. CONCLUSIONS    To our knowledge, this is the largest cohort of Polish patients deficient in natural anticoagulants and evaluated for the causal genetic background. Several new Polish detrimental mutations were detected, mostly in AT- and PC‑deficient patients.

Genetic Risk Factors in Venous Thromboembolism

Genetic risk factors predispose to thrombophilia and play the most important etiopathogenic role in venous thromboembolism (VTE) in people younger than 50 years old. At least one inherited risk factor could be found in about half of the cases with a first episode of idiopathic VTE.Roughly, genetic risk factors are classified into two main categories: loss of function mutations (such as deficiencies of antithrombin, protein C, protein S) and gain of function mutations, (such as prothrombin mutation G20210A, factor V Leiden). A revolutionary contribution to the genetic background of VTE was brought by the achievements of the genome-wide association studies which analyze the association of a huge number of polymorphisms in large sample size.Hereditary thrombophilia testing should be done only in selected cases. The detection of hereditary thrombophilia has impact on the management of the anticoagulation in children with purpura fulminans, pregnant women at risk of VTE and may be useful in the assessment of the risk for recurrent thrombosis in patients presenting an episode of VTE at a young age (<40 years) and in cases with positive family history regarding thrombosis.

The utility of thrombophilia testing

In the past decades, the recognition of several inherited thrombophilic traits has greatly improved our knowledge of the pathogenesis of venous thromboembolism, explaining about half of all idiopathic cases. As a consequence, thrombophilia testing has enormously increased in the past years for various clinical conditions. In this paper, the current indications of the most commonly tested thrombophilic abnormalities (i.e., Factor V Leiden, prothrombin G20210A mutation, protein C, S and antithrombin deficiencies) are analysed. When used appropriately thrombophilia testing has a positive impact on the health care of the people tested and their relatives.

Genetic variants in Cell Adhesion Molecule 1 (CADM1): a validation study of a novel endothelial cell venous thrombosis risk factor

INTRODUCTION

In a protein C deficient family, we recently identified a candidate gene, CADM1, which interacted with protein C deficiency in increasing the risk of venous thrombosis (VT). This study aimed to determine whether CADM1 variants also interact with protein C pathway abnormalities in increasing VT risk outside this family.

MATERIALS AND METHODS

We genotyped over 300 CADM1 variants in the population-based MEGA case-control study. We compared VT risks between cases with low protein C activity (n=194), low protein S levels (n=23), high factor VIII activity (n=165) or factor V Leiden carriers (n=580), and all 4004 controls. Positive associations were repeated in all 3496 cases and 4004 controls.

RESULTS

We found 22 variants which were associated with VT in one of the protein C pathway risk groups. After mutual adjustment, six variants remained associated with VT. The strongest evidence was found for rs220842 and rs11608105. For rs220842, the odds ratio (OR) for VT was 3.2 (95% CI 1.2-9.0) for cases with high factor VIII activity compared with controls. In addition, this variant was associated with an increased risk of VT in the overall study population (OR: 1.5, 95% CI 1.0-2.2). The other variant, rs11608105, was not associated with VT in the overall study population (OR: 1.0, 95% CI 0.8-1.1), but showed a strong effect on VT risk (OR: 21, 95% CI 5.1-88) when combined with low protein C or S levels.

CONCLUSIONS

In a population-based association study, we confirm a role for CADM1 variants in increasing the risk of VT by interaction with protein C pathway abnormalities.

No impact of endogenous prothrombotic conditions on the risk of central venous line-related thrombotic events in children: results of the KIDCAT study (KIDs with Catheter Associated Thrombosis)

BACKGROUND AND OBJECTIVE

Central venous lines (CVLs) are the major exogenous risk factor for deep venous thrombosis (DVT) in children. The study objective was to assess whether endogenous prothrombotic conditions contribute to the risk of CVL-related DVT in children.

METHODS

This was a cohort study of consecutive children with heart disease requiring CVLs for perioperative care. CVLs were inserted percutaneously in the upper venous system and patients received prophylaxis with continuous unfractionated heparin (50 u kg(-1)  d(-1) ). Blood samples to test for prothrombotic conditions were collected prospectively and assayed in a blinded fashion. Outcome assessment was by screening for DVT by venography, venous ultrasound and echocardiography.

RESULTS

The study population consisted of 90 children, median age 2.7 years (0 months-18 years). Prevalence rates of antithrombin deficiency, protein C deficiency, protein S deficiency, heterozygous factor V Leiden, prothrombin G20210A mutation, methylentetrahydrofolate C677TT genotype, hyperhomocysteinemia, lupus anticoagulant, anticardiolipin antibodies and increased levels of lipoprotein (a) were within the range reported for the general population. At least one prothrombotic condition was present in 38% of children and combined abnormalities in 8%. The incidence of DVT was 28% (25/90), and most DVTs were asymptomatic. None of the prothrombotic conditions showed a significant association with DVT. The population attributable risk (i.e. the risk of DVT in the overall population attributable to a specific condition) did not exceed 2.2%.

CONCLUSION

Prothrombotic conditions did not have an important impact on the risk of DVT in children with short-term CVLs. The results of the study suggest that screening for prothrombotic conditions is not justified in this setting.

[Analysis of a hereditary protein C deficient consanguineous pedigree caused by Phe139Val homozygous mutation]

OBJECTIVE

To analyze genetic mutation and explore its molecular pathogenesis for an hereditary protein C (PC) deficient consanguineous pedigree.

METHODS

The pedigree included three generations and contained eight members. PC activity (PC:A), PC antigen (PC:Ag) and other coagulant parameters were detected for all family members. Protein C gene (PROC) include all the exons and intron exon boundaries were amplified by PCR for the proband, then analyzed by direct sequencing. Mutation sites were detected for the other family members.

RESULTS

The PC:A and PC:Ag in the proband plasma were 20% (normal range 70% -140%) and 13.2% (normal range 70%-130%). A homozygous missense mutation g.6128T>G in exon 7 resulting in Phe139Val was identified in the proband. The PC:A and PC:Ag in her younger brother were 31% and 18.90%, Phe139Val homozygous was also found. The left family members were heterozygous for Phe139Val.

CONCLUSION

Phe139Val homozygous missense mutation in exon 7 of PROC caused serious hereditary protein C deficiency. We speculated that homozygous mutation might be resulted from this consanguineous marriage.

Protein C and protein S deficiency - practical diagnostic issues

Protein C (PC) and protein S (PS) are vitamin K-dependent glycoproteins, that act as natural anticoagulants. The proteolytic activation of PC by thrombin occurs on the surface of endothelial cells and involves thrombomodulin and endothelial PC receptor. In the presence of PS, phospholipids and calcium, activated PC (APC) inactivates membrane bound factors V (FVa) and FVIIIa by their cleavage at the specific arginine residues. PC and PS deficiencies are inherited as autosomal dominant disorders associated with recurrent venous thromboembolism (VTE) and, in most cases, derived from heterozygous missense mutations (78% and 63%, respectively). Heterozygous PC deficiency is found in 6% of families with inherited thrombophilia, in 3% of patients with a first-time deep vein thrombosis (DVT) and 0.2-0.3% of healthy individuals. The PS deficiency is detected more commonly than PC deficiency and its prevalence has been estimated with a less than 0.5% in the general European population and 2% to 12% of selected groups of thrombophilic patients. Approximately 75% of PC-deficient patients have type I deficiency and 95% of PS-deficient patients develop type I and type III of PS deficiency. The diagnosis of PC and PS deficiencies is challenging, many preanalytical and analytical factors may affect the PC/PS levels. Molecular analysis of the PC and PS genes (PROC and PROS1, respectively) involves direct gene sequencing and if negative, multiplex ligation-dependent probe amplification (MLPA) method. Patients with low PC and PS levels and the known mutation within PROC or PROS1 genes combined with other genetic or environmental thrombosis factors are at increased risk of recurrent thromboembolic events and require lifelong oral anticoagulation.

Protein C

Protein C (PC) is a 62-kDa vitamin K-dependent plasma zymogen which, after activation to serine protease, plays an important role in the physiologic regulation of blood coagulation. Given that PC is one of the major naturally occurring inhibitors of coagulation, acquired or hereditary deficiencies of this protein result in excessive thrombin generation. As a vast array of mutations are responsible for hereditary PC deficiencies, screening for their presence by DNA testing would require sequencing each entire gene involving numerous exons. Moreover, the knowledge of the gene mutation does not offer any benefit in the treatment of thrombophilic families, so the routine molecular characterization is not indicative. These defects are detected by functional or immunological assays. Measurement of PC activity is essential to identify subjects with both type I and type II PC defects. There is no need to routinely perform PC immunological assays. However, they are useful in order to distinguish type I from type II PC hereditary deficiency.

[Analysis of an hereditary protein C deficiency pedigree with compound heterozygous gene mutations]

OBJECTIVE

To analyze genetic mutations and explore its molecular pathogenesis for an hereditary protein C (PC) deficiency pedigree.

METHODS

The pedigree has included 15 individuals from 4 generations. Plasma levels of PC activity (PC:A), PC antigen (PC:Ag) and other coagulant parameters were determined for members of the family. The 9 exons and intron-exon boundaries of protein C gene (PROC) of the proband were amplified with PCR and analyzed with direct sequencing. Detected mutations were confirmed with reverse sequencing. Corresponding PCR fragments from the family members were also directly sequenced.

RESULTS

Plasma PC:A and PC:Ag for the proband was 26% and 18.60%, respectively, both being lower than normal references. Seven members from the pedigree also had lower PC:A, six had lower PC:Ag. A compound heterozygous missense mutation, including a T to G transition at position 6128 of exon 7, which results in Phe139Val, and a G to C transition at position 8478 in exon 9, which results in Asp255His, were identified in the proband. The paternal grandma, father and two aunts were heterozygous for g.6128 T to G, whilst the mother, the second uncle, sister and son were heterozygous for g.8478 G to C. There were lower PC:A in family members with g.8478 G to C.

CONCLUSION

The proband had inherited two independent mutations of the PROC gene including g.6128 T to G in exon 7 and g.8478 G to C in exon 9 from her father and mother, respectively. The resulting compound heterozygous mutation has caused a serious hereditary protein C deficiency.

PROC c.574_576del polymorphism: a common genetic risk factor for venous thrombosis in the Chinese population

BACKGROUND

There are ethnic differences in the genetic risk factors for venous thrombosis (VT). The genetic causes of VT in the Chinese population are not fully understood.

OBJECTIVES

To identify possible common abnormal factors that could contribute to thrombosis susceptibility.

METHODS/RESULTS

We measured the levels of nine types of plasma coagulation factor, three types of anticoagulation factor and two types of fibrinolytic factor in 310 VT patients. Factor V activity was higher in 32 cases. Eleven of the 32 cases also had low protein C (PC) or protein S (PS) activities, indicating PC or PS deficiency. No other abnormalities were observed in the other 21 cases. All of the samples were sensitive to activated PC inactivation. Therefore, the abnormal factor involved may be FV inactivator or its cofactor rather than FV itself. Resequencing identified a common PROC c.574_576del variant in 10 of the 32 subjects. In a case-control study, this variant was detected in 68 of the 1003 patients and in 25 of the 1031 controls. It had an adjusted odds ratio of 2.71 (95% confidence interval [CI] 1.68-4.36). PC amidolytic activities of most variant carriers were similar to those of non-carriers, but the mean anticoagulant activity was only 72.7 U dL(-1). Expression studies in vitro showed that the anticoagulant activity of the mutant PC was 43.6% of that of the wild-type PC.

CONCLUSIONS

We identified what is, so far, the most common genetic risk factor for VT in the Chinese population, with its prevalence being approximately 2.36%.

[A survey of 20 inherited protein C deficiencies in the patients with venous thromboembolism]

OBJECTIVE

To investigate the incidence of inherited protein C deficiency in the patients with venous thromboembolism (VTE).

METHODS

From Apr. of 2010 to Apr. of 2011, 106 patients with VTE totally from Renji hospital were surveyed by a series of laboratory tests including clinical biochemistry tests, coagulation factors activities and anticoagulation factors activities. PROC gene mutations were screened by PCR-direct sequencing in the 20 patients with decreased PC activity.

RESULTS

Among the 20 patients with decreased PC activity, the median activity of factor II, V, VII, VIII, IX, X, XI, XII were 97.0%, 199.9%, 105.5%, 254.7%, 106.4%, 150.4%, 123.1%, 89.9%, respectively.6 PROC gene mutations were found in 11 patients. Six patients have the same point mutation (c.565C > T), the other five mutations were c.508G > T, c.524G > A, c.1174G > A, c.1157T > C, c.577-579del. All of the six mutations were heterozygous, while the c.508G > T, c.524G > A and c.1157T > C were novel in the world.

CONCLUSIONS

In this study, we found that PC deficiency is the major inherited risk factor of VTE. The most common PROC mutation identified in this study was heterozygous c.565C > T missense mutation., c.508G > T, c.524G > A and c.1157T > C were novel PROC mutation. The activities of factor V and VIII were elevated dramatically among VTE patients, which may be correlated to the disease.

Genetic background analysis of protein C deficiency demonstrates a recurrent mutation associated with venous thrombosis in Chinese population

Background

Protein C (PC) is one of the most important physiological inhibitors of coagulation proteases. Hereditary PC deficiency causes a predisposition to venous thrombosis (VT). The genetic characteristics of PC deficiency in the Chinese population remain unknown.

Methods

Thirty-four unrelated probands diagnosed with hereditary PC deficiency were investigated. PC activity and antigen levels were measured. Mutation analysis was performed by sequencing the PROC gene. In silico analyses, including PolyPhen-2, SIFT, multiple sequence alignment, splicing prediction, and protein molecular modeling were performed to predict the consequences of each variant identified. One recurrent mutation and its relative risk for thrombosis in relatives were analyzed in 11 families. The recurrent mutation was subsequently detected in a case (VT patients)-control study, and the adjusted odds ratio (OR) for VT risk was calculated by logistic regression analysis.

Results

A total of 18 different mutations, including 12 novel variants, were identified. One common mutation, PROC c.565C>T (rs146922325:C>T), was found in 17 of the 34 probands. The family study showed that first-degree relatives bearing this variant had an 8.8-fold (95%CI = 1.1–71.6) increased risk of venous thrombosis. The case-control (1003 vs. 1031) study identified this mutation in 5.88% patients and in 0.87% controls, respectively. The mutant allele conferred a high predisposition to venous thrombosis (adjusted OR = 7.34, 95%CI = 3.61–14.94). The plasma PC activity and antigen levels in heterozygotes were 51.73±6.92 U/dl and 75.17±4.84 U/dl, respectively.

Conclusions

This is the first study on the genetic background of PC deficiency in the Chinese population. The PROC c.565C>T mutation is the most frequent cause of PC deficiency as well as a prevalent risk factor for VT in Chinese individuals. The inclusion of this variant in routine thrombophilic detection may improve the diagnosis and prevention of venous thrombosis.

Hypercoagulable states

Hypercoagulable states can be inherited or acquired. Inherited hypercoagulable states can be caused by a loss of function of natural anticoagulant pathways or a gain of function in procoagulant pathways. Acquired hypercoagulable risk factors include a prior history of thrombosis, obesity, pregnancy, cancer and its treatment, antiphospholipid antibody syndrome, heparin-induced thrombocytopenia, and myeloproliferative disorders. Inherited hypercoagulable states combine with acquired risk factors to establish the intrinsic risk of venous thromboembolism for each individual. Venous thromboembolism occurs when the risk exceeds a critical threshold. Often a triggering factor, such as surgery, pregnancy, or estrogen therapy, is required to increase the risk above this critical threshold.

[A pedigree analysis of pulmonary embolism caused by compound heterozygous mutations of protein C]

OBJECTIVE

To study the molecular pathogenesis of protein C (PC) deficiency in a patient with pulmonary embolism and in his family members.

METHODS

Anticoagulated blood samples were collected from the proband and his family members to detect PC, PS and AT activities. PC antigen level was measured using ELISA. The genomic DNA was extracted to amplify all the 9 exons and their flanking sequences of PC gene using PCR, and the PCR products were sequenced. The mutated exons identified were amplified and sequenced for the other family members.

RESULTS

The proband and his parents and sister were identified as carriers of PC gene mutation, which led to type II PC deficiency. Sequencing of the proband's PC gene showed two heterozygous point mutations in exon 3 (G5540A) and exon 7 (C10230T) to cause compound heterozygous mutations of PC E29K and PC R147W, which were inherited from his father and mother, respectively. His sister was a heterozygote of PC R147W.

CONCLUSION

The proband is a compourd heterozygous mutations carrier of PC E29K and PC147W. PC E29K is a novel PC mutation, and PC R147W is a reported PC gene mutation seen in patients with type II hereditary PC deficiency and recurrent thrombosis.

Genome scan of clot lysis time and its association with thrombosis in a protein C-deficient kindred

BACKGROUND

 Previously, we found increased clot-lysis time (CLT), as measured with a plasma-based assay, to increase the risk of venous thrombosis in two population-based case-control studies. The genes influencing CLT are as yet unknown.

PATIENTS/METHODS

 We tested CLT as risk factor for venous thrombosis in Kindred Vermont II (n = 346), a pedigree suffering from a high thrombosis risk, partially attributable to a type I protein C deficiency. Furthermore, we tested for quantitative trait loci (QTLs) for CLT, using variance component linkage analysis.

RESULTS

 Protein C-deficient family members had shorter CLTs than non-deficient members (median CLT 67 min vs. 75 min). One standard deviation increase in CLT increased the risk of venous thrombosis 2.4-fold in non-deficient family members. Protein C deficiency without elevated CLT increased the risk 6.9-fold. Combining both risk factors yielded a 27.8-fold increased risk. The heritability of CLT was 42-52%. We found suggestive evidence of linkage on chromosome 11 (62 cM), partly explained by the prothrombin 20210A mutation, and on chromosome 13 (52 cM). Thrombin-activatable fibrinolysis inhibitor genotypes did not explain the variation in CLT.

CONCLUSION

Hypofibrinolysis appears to increase thrombosis risk in this family, especially in combination with protein C deficiency. Protein C deficiency is associated with short CLT. CLT is partly genetically regulated. Suggestive QTLs were found on chromosomes 11 and 13.

A prospective cohort study on the absolute risks of venous thromboembolism and predictive value of screening asymptomatic relatives of patients with hereditary deficiencies of protein S, protein C or antithrombin

BACKGROUND

Absolute risks of venous thromboembolism (VTE) in protein S-, protein C-, or antithrombin-deficient subjects are mainly based on retrospective data. Screening asymptomatic relatives of these patients is disputed, though studies addressing this issue have yet to be conducted.

METHODS

We prospectively followed 382 relatives of 84 probands. Participants were assessed for other thrombophilic defects and occurrence of exogenous risk factors (i.e. surgery/trauma/immobilization, malignancies, use of systemic estrogens, and pregnancy/puerperium). After screening, deficient subjects were advised to use thromboprophylaxis during exogenous risk factors; use of oral contraceptives was discouraged.

RESULTS

Overall annual incidence of VTE was 1.53% (95% CI, 1.00-2.34) in deficient vs. 0.29% (0.13-0.64) in non-deficient relatives; adjusted hazard ratio, 7.0 (95% CI, 2.7-18.0). Annual incidence of unprovoked VTE was 0.95% in deficient vs. 0.05% in non-deficient subjects; age-adjusted hazard ratio, 22.3 (P = 0.003). In contrast, annual incidence of provoked VTE was 0.58% vs. 0.24%; age-adjusted hazard ratio, 2.8 (P = 0.08). Fifty-five (37%) deficient and 80 (34%) non-deficient subjects experienced 91 and 143 exogenous risk factors, respectively, during which six vs. five VTEs (6.6% vs 3.5% per risk-period) occurred, despite the higher compliance with recommended thromboprophylaxis use in deficient (51%) vs. non-deficient (22%) subjects. In deficient subjects all provoked VTEs occurred when thromboprophylaxis was not used.

CONCLUSIONS

Protein S, protein C or antithrombin deficiencies confer high absolute risk of VTE. Screening and subsequent augmentation of thromboprophylaxis use may result in reduction of provoked VTE, whereas risk of unprovoked VTE could not be affected by screening.

Laboratory tests for protein C deficiency

Hereditary protein C deficiency is a hypercoagulable state associated with an increased risk for venous thrombosis. The recommended initial test for protein C is an activity (functional) assay, which may be clotting time based or chromogenic. The advantages and disadvantages of the various testing options are presented. The causes of acquired protein C deficiency are much more common than hereditary deficiency. Therefore, this article describes the appropriate steps to take when protein C activity is low, to confirm or exclude a hereditary deficiency. The causes of falsely normal results are also described, including lupus anticoagulants and direct thrombin inhibitors.